Therapeutic aerosols, which are colloidal solutions dispensed in the form of a mist, are widely used in medical procedures. For example, the discharges from inhalation devices such Metered Dose Inhalers (MDI's) are used to deliver medications which will desensitise or dilate the bronchial passages which permit air movement from the trachea to the lungs. It often is necessary to relieve breathing difficulties associated with a variety of disorders by delivering a measured amount of medication to the site of breathing difficulty.
While oral and intravenous methods can be used inhalation therapy using MDI's has numerous advantages. The therapeutic effect is a more rapid, and a reduced amount of medication usually suffices. In addition, there can be a lower incidence of systemic side effects.
In order to operate suitably as a bronchodilator, or expander of the bronchial passages, an MDI system must ensure that sufficient medication reaches the lungs. This is accomplished by having the colloidal suspension forming an aerosol spray released by an MDI take the form of powder or liquid encapsulated by droplets of propellant.
Since the propellant droplets containing the medicament particles are pressurized, they have an initially rapid discharge velocity. In addition, where the aerosol particles are large and the flow rate is rapid, surface forces tend to agglomerate or increase the sizes of the droplets and particles. Where the droplets are large, much of the medication impacts the oropharynx, which is the central portion of the pharynx between the soft palate and the upper portion of the epiglottis, instead of the bronchial passageways which extend from the trachea below the epiglottis.
The sensory effect of oropharyngeal impact may be deceptive and lead a patient to believe erroneously that suitable medication has been achieved, although the desired bronchial site has not been fully medicated with a required dosage. In addition, the localization of medication in the oropharynx can produce adverse side effects when certain aerosols are used, such as those containing corticosteroids. The undesired side effects can include oropharyngeal candidiasis, which is a mucus infection, or dysphonia, which results in hoarseness and difficulty in speaking.
In order to have proper disposition of aerosolized medication in the lungs, rather than in the mouth, it is necessary to coordinate the aerosol discharge by inhaling slowly and deeply, and by using a breath-hold technique upon the completion of inhalation. Otherwise, a reduced amount of aerosol medicament particles are deposited in the lungs with reduced therapeutic effect.
In various attempts to ensure sufficient aerosolized drug deposits in the lungs, several extension devices have been provided for attachment to MDI's. These extension devices have the objective of permitting inhalation of only smaller and slower moving particles.
One such extension device is disclosed in Makiej, U.S. Pat. No. 4,706,663 ('663), issued Nov. 17, 1987 for PARTICLE CATCHER FOR INHALATION DEVICES, in which a particle catcher is placed directly across the inhalation mouth- or nasalpiece opening. The particle catcher is an injection-molded plastic screen formed integrally with, and along the cross section of one end of a flexible support tube. The injection molded plastic screen includes a structural array of interconnecting elements and openings which are of a prescribed size to limit the size of particles and droplets which can pass through the screen.
Activation of the MDI aerosol canister discharges a medicinal spray in the direction of the screen where the aerosolized medication communicates with the interconnecting elements and openings of the screen. Oropharyngeal impaction is said to be reduced because of screen permeation, accompanied by increased bronchial deposition.
However, the combination of extension devices with MDI's can be cumbersome and bulky, often taking the form of multi-piece chambers, and cone shaped spacers or collapsible bags, which can range in length to 25 centimeters (10 inches) and in volume to 1000 cubic centimeters (61 cubic inches).
Although size reductions have been attempted by some collapsible extension devices, they do not deliver the desired medication unless fully extended.
Accordingly, it is an object of the invention to facilitate aerosol medication, particularly in conjunction with metered dose inhalers (MDI's).
Another object is to achieve enhanced medication using a small, portable metered-dose inhaler extension which is easy to use and yet can effectively discharge medicinal aerosols.
Still another object of the invention is to avoid the need for positioning a screen at the cross-sectional inhalation end of devices. A related object is to avoid the need for screen apertures of a prescribed size in order to prevent through-passage of unsuitable droplets.
A further object of the invention is to avoid the need for a particle catcher in order to reduce the size and velocity of aerosol droplets discharged from inhalation devices. Yet another object is to reduce oropharyngeal impaction while increasing the deposition of aerosolized medicine in the bronchial passageways.
Yet another object is to provide an MDI extension which is small, unobtrusive, simple and inexpensive to fabricate.
A still further object of the invention is to provide inhalation therapy for less coordinated patients that is comparable to the therapeutic achieved by patients with good inhalation skills.